The film was produced and directed by Kurt Neumann and stars David Hedison, Patricia Owens, Vincent Price, and Herbert Marshall.

The film tells the story of a scientist who is transformed into a grotesque human–fly hybrid after a common house fly enters unseen into a molecular transporter with which he is experimenting, resulting in his atoms being combined with those of the insect.

In Montreal, Quebec, scientist André Delambre is found dead with his head and arm crushed in a hydraulic press.

Thinking he knows the truth, Hélène asks François to bring the policeman in charge of the case, Inspector Charas, so that she can explain the circumstances of André's death to them both.

Still, he then proceeds to living creatures, including the family's pet cat (which fails to reintegrate but can be heard meowing somewhere) and a guinea pig.

Communicating only with typed notes and knocking, André tells Hélène that he tried to transport himself, but that a fly was caught in the chamber with him, which resulted in the mixing of their atoms.

Time is running out, and while André can still think like a human, he smashes the equipment, burns his notes, and leads Hélène to the factory.

Knowing that nobody would believe the truth, François and Charas decide to declare André's death a suicide so that Hélène is not convicted of murder.

[7] He showed it to Robert L. Lippert, head of 20th Century Fox's subsidiary B-movie studio, Regal Films.

[3][8] Lippert hired James Clavell to adapt Langelaan's story on the strength of a previous sci-fi spec script at RKO, which had never been produced.

[9] The adaptation remained largely faithful to Langelaan's short story, apart from moving its setting from France to Canada, and crafting a happier ending by eliminating a suicide.

[12] Years later, Vincent Price recalled the cast finding some levity during the filming: "We were playing this kind of philosophical scene, and every time that little voice [of the fly] would say 'Help me!

[15] The film was a commercial success, grossing $3 million at the domestic box office against a budget less than $500,000,[4] and becoming one of the biggest hits of the year for Fox studios.

But the film soon becomes as nauseating as its bare outline suggests; even the moments which in healthier pictures might provoke a laugh through sheer absurdity offer little relief".

[18] The New York Times critic Howard Thompson was more positive, writing: "It does indeed contain, briefly, two of the most sickening sights one casual swatter-wielder ever beheld on the screen...

[20] "A first rate science-fiction-horror melodrama", declared Harrison's Reports, adding, "the action grips one's attention from the opening to the closing scenes, and is filled with suspenseful, spine-chilling situations that will keep movie-goers on the edge of their seats".

The film holds a 95% "Fresh" rating on Rotten Tomatoes based on 42 reviews, with the consensus: "Deliciously funny to some and eerily presicient to others, The Fly walks a fine line between shlocky fun and unnerving nature parable".

[23] Cinefantastique's Steve Biodrowski declared that "the film, though hardly a masterpiece, stands in many ways above the level of B-movie science fiction common in the 1950s".

[12] Critic Steven H. Scheuer praised it as a "superior science-fiction thriller with a literate script for a change, plus good production effects and capable performances".

[12] The Fly was nominated for the 1959 Hugo Award for Best SF or Fantasy Movie at the 17th World Science Fiction Convention.